Three-phase reluctance type electric motor

ABSTRACT

A three-phase reluctance type electric motor wherein a magnetic attraction force acts on a rotor in one direction and is not cancelled, thereby reducing mechanical vibration. Since the number of magnetic poles and salient poles is small, a small electric motor of small output power can be obtained. Reduction in the service life of the motor due to the magnetic attraction force acting on the bearings can be prevented by disposing three motors in the same casing. This causes the magnetic attraction force in a radial direction due to the central motor and the magnetic attraction forces in a radial direction due to the two outer motors to act in opposite directions and thus provides balance and maintains a preset attraction force. Every two of the magnetic poles of each phase define a N and S pole pair and a motor of high output torque and high efficiency can be obtained. A reverse current prevention diode is connected in a forward direction of a DC power source so that stored magnetic energy on an excitation coil can be prevented from being fed back to the DC power source when energization of the excitation coil is interrupted, and so that the magnetic energy is caused to flow into an excitation coil to be next energized. Therefore, the excitation current falls and rises rapidly so that generation of counter torque and reduced torque can be suppressed, thereby providing a motor of high efficiency.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a three-phase reluctance type electricalmotor, which is used as a driving source instead of a conventional DCmotor and an induction motor having an inverter, and which is usedparticularly when a motor of a small diameter and small output torque isrequired or when a narrow and long type motor having a large outputpower and less vibration is necessary.

2. Description of the Related Art

A reluctance type electric motor is well known in the art and it canprovide a large output torque. Although it has been used in a robot armas a direct driving device for a load, no such a device is available onthe market and put into practice since the rotation of speed thereof isextremely low.

The motor is sometimes used as a small stepping motor, but wideapplication thereof is not yet found.

SUMMARY OF THE INVENTION

As the first subject problem to be solved by this invention, there is aproblem that the reluctance type motor generates large amount ofmechanical vibration and noise caused by the mechanical vibration. Adetailed explanation thereof is made later.

As the second subject problem, there is a problem that, in thereluctance type motor, magnetic flux between magnetic and salient polesfor generating rotation torque flows into other magnetic and salientpoles to generate counter torque since the salient pole of a rotor andthe magnetic pole producing a field are set substantially in ashort-circuited state (because a gap between the salient pole and themagnetic pole is small) magnetic path. Therefore, a problem occurs inthat the output torque is reduced and the efficiency is lowered.

As a third subject problem, there is a problem that a reluctance typesemiconductor motor cannot be formed to have a large number of phasesunlike an ordinary commutator motor. This is because the price of thesemiconductor circuit on each phase is high and it becomes lesspractical.

Therefore, stored magnetic energy of each magnetic pole increases and ittakes a long time to discharge and store the magnetic energy, and aproblem occurs in that high speed cannot be attained although hightorque can be attained.

As the fourth subject problem, there is a problem that it is difficultto construct a reluctance type motor of small output power with a smalldiameter because the number of salient poles becomes larger.

Accordingly, an object of this invention is to provide a small sizedthree-phase reluctance type electric motor of high speed and high torquein which generation of mechanical vibration and noise can be suppressedin the driving operation.

According to this invention a three-phase reluctance type electric motorof three-phase half-wave energization type comprise a fixed armaturehaving an outer peripheral surface fixed on an outer casing; a rotationshaft rotatably supported by bearings disposed on both sides of theouter casing; a magnetic rotor fixed on the rotation shaft; eightsalient poles of the same height formed to project to the outerperipheral surface of the magnetic rotor, having a width of 180electrical degrees and disposed at a regular pitch; first-phase magneticpoles formed to project from the inner peripheral surface of the fixedarmature, having a width of 180 electrical degrees and separated by thesame angle, the end portions thereof facing the salient poles with asmall gap set therebetween and every two of the first-phase magneticpoles constituting a pair; second- and third-phase magnetic poles havingthe same construction as the first-phase magnetic poles and disposed tobe sequentially separated from the first-phase magnetic poles by 120mechanical degrees; a position detecting unit for detecting the positionof the salient poles of the magnetic rotor by use of position detectingelements to generate a first position detection signal of first-phaserectangular wave and to generate second and third position detectionsignals of the same waveform and of the second and third phases whichare successively generated with a width of 120 electrical degrees;first-, second- and third-phase exciting coils wound on the first-,second- and third-phase magnetic poles; switching elements connected toboth ends of the first-, second- and third-phase exciting coils; firstdiodes respectively connected in a reverse direction to series-connectedcircuits of the switching elements and corresponding ones of theexciting coils; an energization controlling circuit for setting theswitching elements corresponding to the first-, second-and third-phaseexciting coils in the conductive state for periods of time correspondingto the widths of the first, second and third position detection signalsto energize the corresponding exciting coils using a DC power source,thereby generating a driving torque; means for adjusting the position ofthe position detecting element and for fixing the same in position onthe fixed armature side so as to cause the output torque generated byenergization of each phase of the exciting coils to be maximum and flat;and means for rapidly transferring magnetic energy stored in theexciting coil of a preceding stage into stored magnetic energy of theexciting coil of a next stage in a boundary portion between the adjacentposition detection signals using a second diode for prevention ofreverse current coupled to the DC power source in a forward direction soas to suppress torque reduction due to the rising portion in the initialperiod of energization of each exciting coil and to suppress generationof counter torque due to the extension of a falling portion in theterminal period thereof.

Further, according to this invention a three-phase reluctance typeelectric motor characterized by comprises an outer casing having sideplates on both sides thereof; a rotation shaft rotatably supported bymeans of bearings mounted on the central portions of the respective sideplates; a magnetic rotor fixed on the rotation shaft; eight salientpoles of the same height formed to project to the outer peripheralsurface of the magnetic rotor, having a width of 180 electrical degreesand disposed at a regular pitch; first, second and third fixed armaturessequentially arranged in a lateral direction and having outer peripheralportions fixed on the outer casing; first-phase magnetic poles of thefirst fixed armature formed to project from the inner peripheral surfaceof the first fixed armature, having a width of 180 electrical degreesand separated by the same angle, the end portions thereof being set toface the salient poles with a small gap disposed therebetween and everytwo of the first-phase magnetic poles constituting a pair; second- andthird-phase magnetic poles of the first fixed armature having the sameconstruction as the first-phase magnetic poles of the first fixedarmature and disposed to be sequentially separated from the first-phasemagnetic poles of the first fixed armature by 120 mechanical degrees;first-, second- and third-phase magnetic poles of the third fixedarmature formed to project from the inner peripheral surface of thethird fixed armature, disposed in the position of the same phase as eachmagnetic pole of the first fixed armature and having the sameconstruction as each magnetic pole of the first fixed armature; first-,second- and third-phase magnetic poles of the second fixed armatureformed to project from the inner peripheral surface of the second fixedarmature, having the same construction as each magnetic pole of thefirst fixed armature, disposed to have phases deviated by 180 mechanicaldegrees and having a width in a direction of the rotation shaft equal totwice that of the magnetic pole of the first fixed armature; a first-,second- and third-phase exciting coils wound on the first-, second- andthird-phase magnetic poles of each of the first, second and third fixedarmatures; a position detecting unit for detecting the position of thesalient poles of the magnetic rotor by use of position detectingelements to generate a first position detection signal of first-phaserectangular wave and to generate second and third position detectionsignals of the same waveform and of the second and third phases whichare successively generated with a width of 120 electrical degrees;switching elements connected to both ends of the first-, second- andthird-phase exciting coils; first diodes respectively connected in areverse direction to series-connected circuits of the switching elementsand the corresponding exciting coils; an energization controllingcircuit for setting the switching elements corresponding to thefirst-second- and third-phase exciting coils in the conductive stage forrespective periods of time corresponding to the widths of the first,second and third position detection signals to energize thecorresponding exciting coil using of a DC power source, therebygenerating a driving torque; means for adjusting the position of theposition detecting element and for fixing the same in position on thefixed armature side so as to cause the output torque generated byenergization of each of phase of the exciting coils to be maximum andflat; means for rapidly transferring magnetic energy stored on theexciting coil of a preceding stage into stored magnetic energy of theexciting coil of a next stage in a boundary portion between the adjacentposition detection signals by means of a second diode for prevention ofreverse current coupled to the DC power source in a forward direction soas to suppress torque reduction due to the rising portion in the initialperiod of energization of each exciting coil and to suppress generationof counter torque due to the extension of a falling portion in theterminal period thereof; and means for causing the sum of the magneticattraction forces in a direction of the diameter between the salientpoles and the magnetic poles of the first and third fixed armatures andthe attraction force in a direction of the diameter between the salientpoles and the magnetic poles of the second armature to act in theopposite directions and maintaining a preset difference therebetween.

According to this invention, an electric motor having a small diametercan be obtained by setting the number of magnetic poles and salientpoles less than that of the magnetic poles and salient poles of theconventional motor in a case where the motor is a small output powermotor (the output power is equal to or less than 50 Watt). In a case ofa large output power motor, a motor is formed to have a narrow and longstructure, and the first and fourth subject problems discussed above aresolved by using a combination of three motors as in an embodiment shownin FIG. 9.

More specifically, the function of the device of this invention is tosuppress generation of mechanical vibration due to the magneticattraction force acting between the salient poles and the magnetic polesin the diameter direction and having no relation with the output torque.

Generally, general means, means for canceling the above magneticattraction force is sought to be cancelled by disposing the magneticpoles of the same phase in symmetrical positions with respect to therotation shaft.

However, since the length of a gap between the magnetic pole and thesalient pole is approx. 0.1 to 0.2 mm, the gap length becomesnon-uniform in the case of mass production and generation of mechanicalvibration cannot be prevented.

The device of this invention is so constructed that the rotor may alwaysreceive the magnetic attraction force in a preset direction to suppressmechanical vibration without canceling the magnetic attraction force.

At the same time, since the number of magnetic poles and salient polesis set to be less than that of the conventional case, a small motor ofsmall output power can be constructed is attained by.

In a case of a large output power motor, there occurs a problem that themagnetic attraction force acts on the bearing to reduce the service lifethereof.

The above problem can be solved by disposing three three-phasereluctance type motors in the same casing, causing the magneticattraction force (in the diameter direction) by the central one of thereluctance type motors and the magnetic attraction forces by tworeluctance type motors on both sides of the central motor to act inopposite directions so as to set them in balance and maintain presetattraction force.

Every two of the magnetic poles of each phase constitute a pair and thetwo magnetic poles are excited to become N and S poles so as to solvethe second subject problem.

Since the reverse current prevention diode is connected in a forwarddirection to the application DC power source, the stored magnetic energyon an excitation coil can be prevented from being fed back to the powersource side by the above diode when energization of the excitation coilis interrupted and the magnetic energy is caused to flow into anexcitation coil to be next energized and stored therein.

Therefore, fall and rise of the excitation current occur rapidly so thatgeneration of counter torque and reduced torque can be suppressed,thereby providing an electric motor of high efficiency.

As a result, the third subject problem can be solved.

For this reason, this invention has the following effect.

Generation of mechanical vibration and noise during the operation can beprevented. Further, in a case of a motor of small output power, thenumber of salient poles is set to eight, and a small motor of smalloutput power can be obtained.

Further, the rotation speed can be controlled by an application voltagehigher than the counter-electromotive force, that is, by a low voltage,and the output torque can be controlled independently by the excitationcurrent so that a reluctance type motor of high speed and large torquecan be freely designed the application thereof.

As a result, this invention provides an effective DC motor. Inparticular, since the rotor is simply formed of a laminated body ofsilicon steel plates, it can be formed with the narrow and longstructure as shown in FIG. 9 and the inertia thereof becomes small.

Further, output torque of not less than that obtained by using a rotorof expensive rare earth magnet can be attained by this invention withoutusing a rotor of such an expensive rare earth magnet.

Since an excitation current which is ineffective with respect to theoutput torque is interrupted, the efficiency can be enhanced.

Since the rotation speed and output torque can be freely andindependently changed, the torque and rotation speed characteristics canbe improved.

Next, when the torque is set to be high, particularly in the reluctancetype motor, the inductance of the excitation coil becomes large, therebygenerating a counter torque and lowering the speed.

In order to solve the above problem and attain the high speed and largetorque characteristics, a diode 18 is used to rapidly process themagnetic energy stored in the excitation coil and restrict theexcitation current curve within the width of 180 degrees.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an explanatory view of the construction of a three-phasehalf-wave reluctance type electric motor according to this invention;

FIG. 2 is a developed view of a rotor, magnetic pole and excitation coilof the above motor;

FIG. 3 is an explanatory view of the arrangement of a magnetic pole,excitation coil and salient pole of the motor of FIG. 9;

FIG. 4 is a schematic diagram of an electrical circuit for deriving aposition detection signal from the coil;

FIGS. 5 and 6 are schematic diagrams of an energization circuit for theexcitation coil;

FIGS. 7 and 8 are timing charts of position detection signals,excitation current and output torque; and

FIG. 9 is a cross sectional view of another embodiment of a deviceaccording to this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

There will now be described an embodiment of this invention withreference to the accompanying drawings.

FIG. 1 is a plan view showing the construction of exciting coils andmagnetic poles of the fixed armature and salient poles of the rotor of athree-phase reluctance type electric motor according to this invention.The angle used hereinafter is indicated by an electrical angle.

The width of salient poles 1a, 1b, . . . of the rotor is 180 degrees andthe salient poles are disposed at the same pitch with a phase differenceof 360 degrees. The rotor 1 is constructed in a manner which is known inthe art and formed by laminating silicon steel plates, and has arotation shaft 5.

Magnetic poles 16a, 16b, 16c, 16d, 16e and 16f are formed on the fixedarmature 16 to project therefrom.

The width of the salient poles 1a, 1b, . . . and the width of themagnetic poles 16a, 16b, 16c, 16d, 16e and 16f are set to the same valueof 180 degrees. The number of salient poles is 8 and the number ofmagnetic poles is 6.

The armature 16 is also constructed in the same manner as the rotor 1.

The magnetic poles 16a and 16b are separated by 180 degrees, and themagnetic poles 16c and 16d and the magnetic poles 16e and 16f are alsoseparated by 180 degrees. The magnetic poles 16a and 16b, the magneticpoles 16e and 16f and the magnetic poles 16c and 16d respectivelyconstitute first-, second- and third-phase magnetic poles.

Exciting coils 17a and 17b, exciting coils 17e and 17f and excitingcoils 17c and 17d which are wound on the respective magnetic poles 16a,16b, 16e, 16f, 16c and 16d constitute first-, second- and third-phaseexciting coils.

FIG. 2 is a developed view of the reluctance type three-phase electricmotor shown in FIG. 1.

Coils 10a, 10b and 10c are position detection elements for detecting theposition of the salient poles 1a, 1b, . . . , and are fixed on the sideof the armature 16 in the position shown in the drawing and the planesof the coils are set to face the side surfaces of the salient poles 1a,1b, . . . with a gap set therebetween.

The coils 10z, 10b and 10c are separated by 120 degrees. The coils is anair-core coil which has a diameter of 5 mm and 100 turns.

FIG. 4 shows a device for deriving position detection signals by meansof the coils 10a, 10b and 10c.

The coils 10a, 10b and 10c, and resistors 15a, 15b, 15c, . . . , and 15econstitute a bridge circuit, and the coils 10a, 10b and 10c are adjustedto be set in balance when they do not face the salient poles 1a, 1b, . .. .

Accordingly, outputs of low-pass filters constituted by a diode 11a anda capacitor 12a, and a diode 11c and a capacitor 12c become equal and anoutput of an operational amplifier 13a is set to a low level.

An oscillation of approx. 1 MHz is effected by an oscillator 7.

When the coil 10a comes to face any one of the salient poles 1a, 1b, . .. , the impedance is reduced by iron loss (eddy current loss andhysteresis loss) and a voltage drop across the resistor 15a isincreased, thereby setting the output of the operational amplifier 13ato a high level.

When the coils 10b and 10c are set to face the side surfaces of thesalient poles 1a, 1b, . . . , voltage drops across the resistors 15b and15c are increased, outputs of high level can be obtained by inputs to +terminals of the operational amplifiers 13b and 13c via the low-passfilter 11b, 12b and another low-pass filter, respectively.

Output signals from the operational amplifiers 13a, 13b and 13c are usedas position detection signals which are respectively shown by curves25a, 25b, . . . , curves 26a, 26b, . . . and curves 27a, 27b, . . . inthe timing chart of FIG. 8. The above-described three sets of positiondetection signals are sequentially delayed by 120 degrees.

Outputs of differentiating circuits 8a, 8b and 8c shown in FIG. 4 areindicated by electrical signal curves 31a, 31b, . . . , curves 32a, 32b,. . . and curves 33a, 33b, . . . in FIG. 8.

Outputs of terminals 6a, 6b and 6c are set to a low level by means offlip-flop circuits 9a, 9b and 9c by a reset signal when a power sourceswitch is turned on.

If, at this time, an output of the operational amplifier 13a is at ahigh level, the electrical signal 31a can be derived and the output ofthe terminal 6a of the flip-flop circuit 9a is set to a high level.

When the motor is rotated and the output of the operational amplifier13b is set to a high level, the electrical signal 32a (FIG. 8) can bederived and the state of the flip-flop circuit 9a is inverted and theoutput of the terminal 6a is set to a low level.

At the same time, the flip-flop circuit 9b is energized and the outputof the terminal 6b is set to a high level.

Next, when the electrical signal 33a which is a differential pulse ofthe initial portion of the curve 27a of FIG. 8 is derived, the state ofthe flip-flop circuit 9b is inverted and the output of the terminal 6bis set to a low level. Further, the flip-flop circuit 9c is alsoenergized and the output of the terminal 6c is set to a high level.

The operation described above is effected and the outputs of theterminals 6a, 6b and 6c are derived as rectangular position detectionsignals indicated by the curves 28a, 28b, . . . , curves 29a, 29b, . . .and curves 30a, 30b, . . . .

Since the above-described position detection signals are the same asthose derived in a Y-connection DC motor which is well known in the art,the signals can also be derived by use of a means which is known in theart and which uses AND circuits.

However, according to the above means, time gap tends to occur betweenadjacent curves, for example, between the curves 28a and 29a, andtriggering torque cannot be obtained in the three-phase half-waveenergization, thus presenting a problem.

In the circuit of FIG. 4, the flip-flop circuits 9a, 9b and 9c are usedso that the above problem can be solved.

Instead of using the rotor, which the coils 10a, 10b and 10c aredisposed to face, an aluminum plate of the same shape may besynchronously rotated and the coils 10a, 10b and 10c may be disposed toface the projecting portions thereof so as to derive position detectionsignals having the same effect as described above.

The reluctance type motor has an advantage that the output torque can bemade extremely large, but it is prevented from being put into practicebecause of the defects described below.

The first defect is that current cannot be supplied in a reciprocatingmanner to the exciting coil so that the electric circuit may becomeexpensive and the number of magnetic poles and salient poles increasesso that the construction thereof may become complicated.

In a motor according to this invention, a three-phase half-wave motor isused to solve the above problem and at the same time solve problemscaused by half-wave energization.

The second defect is that the torque becomes extremely large in aninitial period of time in which the salient pole starts to face themagnetic pole and becomes small in the termination period of time.Therefore, the resultant torque may contain a large ripple torquecomponent.

The above problem may be effectively solved by use of the followingmeans.

That is, means for making the widths of the opposed surfaces of thesalient pole and the magnetic pole in a direction of the rotation axisdifferent from each other is used.

Leakage flux of the opposite surfaces that may be caused by use of theabove means causes the flat portion of the output torque curve to beincreased as shown by dashed curves 41a, 41b, . . . in the timing chartof FIG. 7 so that the ripple component of the resultant torque can bereduced. The above means will be described later. Thus, the aboveproblem can be solved.

The third defect is that it is only possible to drive the motor at a lowspeed. That is, when the torque is increased, the number of salientpoles and magnetic poles is increased, and when the exciting current isincreased, the rotation speed is significantly lowered and theefficiency becomes low.

In general, in the reluctance type motor, in order to increase theoutput torque, it is necessary to increase the number of salient polesand magnetic poles of FIG. 1 and reduce the gap between the opposedpoles.

At this time, if the rotation speed is kept at a preset value, theinclination of rise of the exciting current is made less steep bymagnetic energy stored in the magnetic poles 16a, 16b, . . . and thesalient poles 1a, 1b, . . . of FIG. 1. Even after the energization isinterrupted, time to terminate the discharge of current is relativelyextended by the magnetic energy and therefore large counter torque isgenerated.

Under this condition, the peak value of the exciting current becomessmall and counter torque is generated so that the rotation speed may beset to a small value. Further, the efficiency becomes low.

According to a motor according to this invention, the above defects canbe eliminated. This is explained later in detail with reference to theembodiment.

The fourth defect is that vibration occurs during the rotation.

In the developed view of FIGS. 1 and 2, the magnetic core 16 which is anannular portion, and the magnetic poles 16a, 16b, . . . are constructedby laminating and solidifying silicon steel plates by a conventionalmethod and fixed on an outer casing which is not shown to form anarmature. The magnetic core 16 provides a magnetic path.

As shown in FIG. 2, the exciting coils 17a, 17b, . . . are mounted onthe magnetic poles 16a, 16b, . . . . The exciting coils 17a and 17b areconnected in series or in parallel and the connected body form anexciting coil K.

The exciting coils 17c and 17d and the exciting coils 17e and 17f areconnected in the same manner to respectively form exciting coils L andM.

When the exciting coil M is energized, the salient poles 1g and 1f areattracted to rotate the rotor 1 in a direction indicated by an arrow A.When it has rotated by 120 degrees, energization of the exciting coil Mis interrupted and then the exciting coil L is energized.

When it is further rotated by 120 degrees, energization of the excitingcoil L is interrupted and then the exciting coil K is energized.

The energization mode is cyclically changed at each rotation of 120degrees in a sequence of the exciting coil K, the exciting coil M andthe exciting coil L and it is driven as a three-phase half-wave motor.

At this time, magnetic poles of each set which are set in each phaseposition are magnetized to the N and S poles as shown in the drawing.

Since the two magnetic poles to be magnetized always have differentpoles, leakage fluxes passing through non-magnetized magnetic poles flowin opposite directions, thereby preventing occurrence of the countertorque.

Next, energization means for the exciting coils K, L and M is explained.

As shown in FIG. 5, transistors 20a, 20b and 20c and transistors 20d,20e and 20f are respectively connected to both ends of the excitingcoils K, L and M.

The transistors 20a, 20b, 20c, . . . are used as switching elements, butother semiconductor elements having the same effect can be used.

Electric power is supplied from the positive and negative terminals 2aand 2b of a DC power source.

If an electrical signal of high level is input from the terminal 4a whena lower side input of the AND circuit 14a is at a high, the transistors20c and 20d and the transistors 20e and 20f are turned on to energizethe exciting coils M and L.

A terminal 40 is a reference voltage terminal for specifying theexciting current. It is possible to change the output torque by changingvoltage of the terminal 40.

When a power source switch (not shown) is turned on, and input to the -terminal of the operational amplifier 40a is lower than that to the +terminal so that an output of the operational amplifier 40a will be setto a high level, and the transistors 20a, 20b, . . . , and 20f, areturned on to apply voltages to the energization circuit of the excitingcoils K, M and L.

A resistor 22 is a resistor for detecting exciting currents in theexciting coils K, M and L.

An input signal to the terminal 4a is provided by the position detectionsignals 28a, 28b, . . . of FIG. 8 and input signals to the terminals 4band 4c are provided by the position detection signals 29a, 29b, . . .and 30a, 30b, . . . .

The above-described curves are indicated by the same symbols in thefirst column in the timing chart of FIG. 7. The curves 28a, 29a, 30a, .. . are continuous.

Next, energization of each exciting coil is explained with reference tothe timing chart of FIG. 7.

When the exciting coil M is energized for a period of time correspondingto the width (which is indicated by an arrow 36 and is a width of 120degrees) of the position detection signal 29a by use of a conventionalmethod, rise of the energization current is delayed as indicated by thefront half portion of a dashed curve 34 because the inductance of theexciting coil M is large.

Further, the falling portion thereof is extended by the discharge oflarge magnetic energy as shown by the latter half portion of the curve34. A period of time of 180 degrees in which positive torque isgenerated is indicated by an arrow 37.

Therefore, in the front half portion of the curve 34, the torque isreduced, and in the latter half portion, large counter torque isgenerated. The fact that the torque is reduced is represented by theexpression that the reduced torque is generated. Therefore, theefficiency is lowered and the rotation is effected at a low speed.

One of the features of a motor according to this invention is that theabove problem can be solved. This is explained below.

When a position detection signal is input from the terminal 4a, theexciting current increases and the exciting current exceeds a presetvalue (specified by the reference voltage of the terminal 40 of FIG. 5),an output of the operational amplifier 40a is set to a low level so thatan output of the AND circuit 14a may be set to a low level, therebyturning off the transistor 20a.

As a result, when the magnetic energy stored in the exciting coil K isdischarged via the diode 21a, the transistor 20b and the resistor 22 anda discharging current has reached a preset value, an output of theoperational amplifier 40a is returned to the high level by thehysteresis characteristic thereof so as to turn on the transistor 20aagain, thereby increasing the exciting current.

When the exciting current is increased to a preset value defined by thereference voltage 40, an output of the operational amplifier 40a is setto the low level so as to turn off the transistor 20a, thereby reducingthe exciting current.

Thus, the circuit functions as a chopper circuit for repeatedlyeffecting the above operation.

In the end portion of the curve 28a, an input to the terminal 4a of FIG.5 is eliminated.

As a result, the magnetic energy stored in the exciting coil K tends tobe fed back to the positive terminal 2a side of the power source via thediodes 21a and 21b since the transistors 20a and 20b are both set in theOFF state, but it is inhibited by the diode 18.

At this time, since an input signal of high level to the terminal 4b ispresent, the transistors 20c and 20d are turned on.

Therefore, the stored magnetic energy in the exciting coil K causes ahigh voltage and flows into the exciting coil M to cause the excitingcurrent to rapidly rise. Further, extinction of the stored magneticenergy can be rapidly effected.

According to the actual measurement, the widths of fall and rise of theexciting current in a motor with an output power of approx. 50 Watt,that is, the widths of fall and rise of the dashed curves 34a and 34bare approximately 15 μsec, and the occurrence of reduced torque andcounter torque can be suppressed even in the high-speed rotation(several tens of thousands revolutions per minute).

The widths of falling portion and rising portion of the curves 34a and34b can be reduced by enhancing the voltage between the terminals 2a and2b and feeding back the stored magnetic energy to the power source sideand thus the same purpose can be attained. However, this requires theapplication DC voltage ten times higher than that set according to thisinvention, and thus is less practical.

Occurrence of the counter torque can be prevented by setting the widthof the falling portion of the curve 34b of FIG. 7 to be less than 30degrees (the width indicated by an arrow 37a).

The above conditions are exactly the same for the other energizationcurves 34b and 34c and the same operation and effect can be attained.

Since the widths of the curves 28a, 29a and 30a become smaller as therotation speed becomes higher, it is necessary to correspondingly reducethe widths of the falling portion and rising portion of the curves 34a,34b and 34c.

The current or output torque can be kept constant by the choppercontrol. In order to increase the output torque, the reference voltage40 of FIG. 5 may be enhanced.

As described above, a motor according to this invention has a featurewherein a limit to the high-speed rotation is controlled by anapplication voltage corresponding to a counter-electromotive force, andthe output torque can be independently controlled by the referencevoltage (specified voltage of the output torque). The control current bythe position detection signal 29 (input signal of the terminal 4b) ofthe exciting coil M varies according to the ON and OFF of the transistor20c as shown by broken lines 34b of FIG. 7 by the chopper effect of theAND circuit 14b and the operational amplifier 40a of FIG. 5 and thenrapidly falls as shown by the broken lines at the end of the curve 29a.

When the position detection signal 30a is next input to the terminal 4cof FIG. 5, energization of the exciting coil L is effected in the samemanner.

As described above, the exciting coils K, M and L are sequentially andcontinuously energized to generate output torque.

As described before, since there is no gap in the boundary portionbetween the signal curves 28a, 29a, . . . of FIG. 7, and one of theexciting coils is energized at startup. Therefore, the startingoperation can be reliably effected.

The diode 18 of FIG. 5 is connected to the positive terminal 2a side ofthe power source, but it is possible to attain the same object byomitting the diode and connecting a reverse current prevention diode 18a(indicated by broken lines) to the negative terminal 2b side of thepower source.

A capacitor 19 is not always necessary but is used to prevent thetransistors 20a, 20b, . . . from being damaged when the ON and OFFoperations of the transistors are delayed. In order to attain the abovepurpose, the capacitance of the capacitor 19 may be set to 0.1 μF.

At the time of low-speed operation of approximately 3000 revolutions perminute, it is not necessary to make the rise and fall of the curves 34a,34b and 34c of FIG. 7 steep so that the capacitance of the capacitor 19may be increased according to the rotation speed.

The chopper control attained by the ON and OFF operations of thetransistors 20a, 20c and 20e has been explained above, but the object ofthis invention can be attained by using a chopper circuit forcontrolling the ON and OFF operations of the transistors 20a and 20b,transistors 20c and 20d, and transistors 20e and 20f according tooutputs of the AND circuits 14a, 14b and 14c, respectively.

Next, the control operation is explained in detail with reference toFIG. 6.

The circuit of FIG. 6 is different from the embodiment of FIG. 5 in thechopper circuit. When a voltage drop occurs across the resistor 22,current in the exciting coil K is small and an input to the + terminalof an operational amplifier 40b is smaller than an input (voltage at thereference voltage terminal 40) to the - terminal thereof, the outputthereof is set to a low level.

Therefore, an output of an inverter circuit 24a is set to a high level,and when input of a position detection signal to the terminal 4a isstarted, an output of an AND circuit 14a is set to a high level to turnon transistors 20a and 20b, thereby increasing current in the excitingcoil K.

When the exciting current has exceeded a preset value, an output of theoperational amplifier 40b is changed to a high level, and therefore, adifferential pulse can be derived from a differentiating circuit 23 andthe differential pulse energizes a monostable circuit 24 so as togenerate an electrical signal of high level of preset time length. Theelectrical signal is inverted by the inverter circuit 24a.

As a result, an output of the AND circuit 14a is changed to a low levelfor a preset period of time and the transistors 20a and 20b are turnedoff.

Magnetic energy stored in the exciting coil K is not fed back to thepower source because of the presence of a diode 18 and charges acapacitor 19.

As described before, since the capacitance of the capacitor 19 is set toapprox. 0.1 μF, the charging operation will be completed in 15 μsec evenwhen the entire magnetic energy stored in the exciting coil K isdischarged and charged. Therefore, the exciting current will rapidlyfall even in this case although the situation is slightly different.

In a case where the length of time for the exciting current to fall by1/100 is 2 μsec, the transistors 20a and 20b can be turned on again toincrease the current in the exciting coil K when the exciting current isreduced by 1/100 by setting the time length of the output of themonostable circuit 24 to 2 μsec.

Since an application voltage set at this time becomes equal to the highvoltage of the capacitor 19, the exciting current rapidly rises, andwhen it has exceeded a preset value specified by the voltage of thereference voltage terminal 40, the transistors 20a and 20b are turnedoff again for the time length of the output of the monostable circuit24. When the exciting current decreases by 1/100, the exciting currentincreases.

The circuit constitutes a chopper circuit for repeatedly effecting theabove operation.

The same chopper operation is effected for the other exciting coils Mand L. The circuit has a feature wherein the chopper frequency can beset higher than that set in the case of the chopper circuit of FIG. 5.

Therefore, a current ripple caused by the chopper circuit or an outputtorque ripple can be reduced.

Further, the chopper frequency can be reduced by increasing thecapacitance of the capacitor 19 and increasing the output width of themonostable circuit 24.

As is clearly understood from the above explanation for the embodimentsof FIGS. 5 and 6, since the number of salient poles and magnetic polesis small, an electric motor of small output power having a smalldiameter can be obtained.

An electric motor of high speed and high efficiency can be obtained byusing the diode 18.

In FIG. 1, the magnetic poles 16a and 16b attract the salient poles 1aand 1b in a direction indicated by an arrow B (in a diameter direction)when the exciting coils 17a and 17b are energized, and then the excitingcoils 17e and 17f are next energized so that the arrow B of attractionforce is rotated by 120 mechanical degrees in a counterclockwisedirection.

As described above, the attraction force of arrow B is rotated in theopposite direction with respect to the rotation of the rotor 1 in thedirection of arrow A, and the rotation shaft 5 is kept pushed againstthe bearings (ball bearings of the shaft 5). Thus, vibration can besuppressed.

As is understood from the above explanation, the defects describedbefore can be solved.

The torque curve (created by the N and S magnetic poles) of a DC motorhaving a magnet rotor is symmetrical, but the torque curve of areluctance type motor is asymmetrical, and the torque becomes extremelylarge in the initial period in which the salient poles start to face themagnetic pole and rapidly decreases in the termination period.

The torque curve may have a flat portion as shown by the curves 41a,41b, . . . in FIG. 7 by setting the widths of the magnetic poles in thedirection of the rotation axis to different values.

However, as is seen from the curves 41a, 41b, . . . , increase in theexciting current.

Therefore, the output torque can be increased and the flatness of theoutput torque characteristic can be improved by setting the startingpoint of energization earlier than the energization (in the casedescribed before) of 120 degrees in the central portion of the torquecurve.

This is explained below with reference to the third-stage timing chartof FIG. 7.

The torque is made flat on the right side of a point indicated by brokenlines C, and the width of the flat portion thereof becomes smaller asthe exciting current increases.

The exciting coil M is explained as an example. The fixed positions ofthe coils 10a, 10b and 10c of FIG. 2 are adjusted so that energizationcan be started near the starting portion of the third-stage torque curveof the timing chart.

Therefore, the exciting current may be indicated by a dashed curve 35b.An arrow 38 indicates the width of the curve 29a which is 120 degrees,and an arrow 39 indicates the width of 180 degrees in which the positivetorque can be obtained.

If the width of the falling portion of the curve 35b is smaller than thearrow 39a, no counter torque is generated. The width is set to be twicethat of the arrow 37a in the first stage, and therefore a motor ofhigher speed can be obtained.

Further, since the length of the flat portion of the output torque isincreased, the output torque ripple can be reduced.

The exciting currents in the other exciting coils K and L indicated bydashed curves 35a and 35c and the effects thereof which are the same asdescribed above can be obtained.

The length of the flat portion of the torque curves 41a, 41b, . . .becomes smaller as the exciting current is larger, that is, the curve ispositioned in the higher position, and it is necessary to increase thelength of the flat portion of the torque by changing the shape of thesalient poles facing the magnetic poles.

As described before with reference to the arrow B of FIG. 1, occurrenceof vibration can be prevented.

However, in the case of a motor having a large output power, since theampere-turn of the exciting coil is large, the attraction force of thearrow B becomes large, thereby presenting a problem in that the servicelife of the ball bearing is reduced.

An embodiment in which the above problem is solved is shown in FIG. 9.

Side plates 42a and 42b are fitted to openings of a metal cylinder 42,and a rotation shaft 5 is rotatably supported by ball bearings 5b and 5amounted to the side plates 42b and 42a, respectively.

The central portions of rotors 1, 1-1 and 1-2 are fixed on the rotationshaft 5. The rotor 1 is shown by the same symbol in the developed viewof FIG. 2.

The rotors 1-1 and 1-2 have salient poles having the same constructionas those of the rotor 1 and the salient poles are arranged in the samephase position. The rotors 1, 1-1 and 1-2 can be integrally formed.

Armatures 16 and 16 are the armature shown in FIG. 2.

An armature 16-1 has the same construction as the armature 16.

The outer peripheral portion of each of the armatures is forcedlyinserted into and fixed inside an outer casing 42. First-, second- andthird-phase magnetic poles of the armatures 16 and 16-1 are set inpositions of the same phase.

The detail of the armature 16 is shown in FIG. 2.

First-, second- and third-phase magnetic poles 16a and 16b, magneticpoles 16e and 16f, and magnetic poles 16c and 16d corresponding to themagnetic poles 16a, 16b, . . . are arranged with deviation of 180mechanical degrees in the right direction.

Projecting portions of the same shape and same phase as the salientpoles 1a, 1b, . . . are formed on the outer periphery of the positiondetection rotor 45 formed of an aluminum plate, position detection coils10a, 10b and 10c are arranged to face the outer peripheral surfacethereof, and position detection signals can be derived by use of thecircuit shown in FIG. 4.

The rotor 1-1 of FIG. 9 having the same construction as the rotor 1 canbe driven in a direction indicated by the arrow A (shown in FIG. 2) bythe above position detection signal and controlling energization ofexciting coils 17a and 17b, exciting coils 17e and 17f, and excitingcoils 17c and 17d used instead of the exciting coils K, M and L by useof the energization controlling circuit of FIG. 6.

The armature 16-1 of FIG. 9 has the same construction as the armature16, and the rotor 1-2 can be driven in a direction of the arrow A byenergizing the exciting coils of the magnetic poles thereof by use ofthe energization controlling circuits of FIGS. 5 and 6.

As a result, the motor 9 can be driven as three three-phase half-waveenergization type motors.

Forces in the direction of the arrow B (shown in FIG. 1) in which therotors 1 and 1-2 are attracted in the diameter direction by the magneticpoles of the armatures 16 and 16-1 act in the same direction.

The vector of force by which the rotor 1-1 is attracted in the diameterdirection by the magnetic poles of the armature 16 is set in a directionopposite to that indicated by the arrow B.

As shown in FIG. 9, a difference between the two vectors in the diameterdirection described above can be set to a small value by setting thewidths of the rotors 1 and 1-2 in the direction of the rotation axisequal to each other and setting the sum of the above widthssubstantially equal to the width of the rotor 1-1.

Therefore, the force by which the rotation shaft 5 depresses the ballbearings 5a and 5b can be reduced. Consequently, bearing damage in amotor of large output power can be eliminated and an vibration isprevented.

FIG. 3 shows the arrangement of the magnetic poles and exciting coils asviewed in the direction of the rotation shaft 5.

The positions of the salient poles 1a, 1b, . . . are shown, the magneticpoles 16a, 16g, . . . and 16f indicate the position of the armature ofFIG. 9. The magnetic poles of the armature 16-1 are also set in the sameposition with the same phase.

The magnetic poles 16a, 16b, . . . , and 16f of the armature 16 are setin positions deviated by 180 mechanical degrees.

The cross section of FIG. 1 taken along the arrow D is shown in FIG. 9.

A motor according to this invention is used as a driving source insteadof an induction motor having an inverter and a DC motor, and isparticularly used in a case where the diameter is small and the outputtorque is small, or where a motor which is narrow and long, whose outputpower is large and in which vibration suppression is required.

I claim:
 1. A three-phase reluctance electric motor, comprising:a fixedarmature having an outer peripheral surface fixed on an outer casing; arotation shaft rotatably supported by bearings disposed on both sides ofsaid outer casing; a magnetic rotor fixed on the rotation shaft; eightsalient poles of the same height formed to project to an outerperipheral surface of said magnetic rotor, having a width of 180electrical degrees and disposed at a predetermined pitch; first-phasemagnetic poles formed to project from an inner peripheral surface ofsaid fixed armature, having a width of 180 electrical degrees andseparated by 180 electrical degrees, having end portions facing saidsalient poles with a predetermined gap between said end portions andsaid salient poles, and two of said first-phase magnetic poles defininga pair; second- and third-phase magnetic poles having the sameconstruction as said first-phase magnetic poles and disposed to besequentially separated from said first-phase magnetic poles by 120mechanical degrees; a position detecting means for detecting a positionof said salient poles of said magnetic rotor, said position detectingmeans including position detecting element means for generating a firstposition detecting signal of a first-phase rectangular wave and secondand third position detecting signals of second-and third-phaserectangular waves, said first, second and third position detectingsignals being successively generated with a width of 120 electricaldegrees; first-, second- and third-phase exciting coils wound on saidfirst-, second- and third-phase magnetic poles; switching elementsconnected to both ends of said first-, second- and third-phase excitingcoils; first diodes respectively connected in a reverse direction toseries-connected circuits of said switching elements and correspondingones of said first-, second- and third-phase exciting coils; anenergization controlling circuit means for setting said switchingelements corresponding to said first-, second- and third-phase excitingcoils in a conductive state for respective periods of time correspondingto the widths of said first, second and third position detecting signalsto energize said corresponding ones of said first-, second- andthird-phase exciting coils, said energization controlling circuit meansincluding DC power source means for generating a driving torque; meansfor adjusting the position of said position detecting means and forfixing the position of said position detecting means so as to cause anoutput torque generated by energization of each of the first-, second-and third-phase exciting coils to be substantially at a maximum andsubstantially flat; and transfer means for rapidly transferring magneticenergy stored on a preceding one of said first-, second- and third-phaseexciting coils into stored magnetic energy of a next one of said first-,second- and third-phase exciting coils in a boundary portion betweenadjacent ones of said first, second and third position detectingsignals, said transfer means including second diode means for preventinga reverse current and coupled to said DC power source means in a forwarddirection so as to suppress torque reduction due to a rising portion inan initial period of energization of each of said first-, second- andthird-phase exciting coils and to suppress generation of a countertorque due to an extension of a falling portion in the terminal periodof each of said first, second- and third-phase exciting coils.
 2. Athree-phase reluctance electric motor, comprising:an outer casing havingside plates on both sides of said outer casing; a rotation shaftrotatably supported by bearings mounted on central portions of said sideplates; a magnetic rotor fixed on said rotation shaft; eight salientpoles of the same height formed to project to an outer peripheralsurface of said magnetic rotor, having a width of 180 electrical degreesand disposed at a predetermined pitch; first, second and third fixedarmatures sequentially arranged in an axial direction and having outerperipheral portions fixed on said outer casing; first-phase magneticpoles of said first fixed armature formed to project from an innerperipheral surface of said first fixed armature, having a width of 180electrical degrees and separated by 180 electrical degrees, having endportions facing said salient poles with a predetermined gap between saidend portions and said salient poles, and two of said first-phasemagnetic poles of said first fixed armature defining a pair; second- andthird-phase magnetic poles of said first fixed armature having the sameconstruction as said first-phase magnetic poles of said first fixedarmature and disposed to be sequentially separated from said first-phasemagnetic poles of said first fixed armature by 120 mechanical degrees;first-, second- and third-phase magnetic poles of said third fixedarmature formed to project from an inner peripheral surface of saidthird fixed armature, each of said first-, second- and third-phasemagnetic poles of said third fixed armature being disposed in a positioncorresponding to corresponding ones of said first-, second- andthird-phase magnetic poles of said first fixed armature and having thesame construction as corresponding ones of said first-, second- andthird-phase magnetic poles of said first fixed armature; first-, second-and third-phase magnetic poles of said second fixed armature formed toproject from an inner peripheral surface of said second fixed armature,each of said first-, second- and third-phase magnetic poles of saidsecond fixed armature having the same construction as corresponding onesof said first-, second- and third-phase magnetic poles of said firstfixed armature, disposed in a position deviated by 180 mechanicaldegrees from corresponding ones of said first-, second- and third-phasemagnetic poles of said first fixed armature and having a width in theaxial direction equal to twice that of corresponding ones of saidfirst-, second- and third-phase magnetic poles of said first fixedarmature; first-, second- and third-phase exciting coils wound on saidfirst-, second- and third-phase magnetic poles of each of said first,second and third fixed armatures; a position detecting means fordetecting a position of said salient poles of said magnetic rotor, saidposition detecting means including position detecting element means forgenerating a first position detecting signal of a first-phaserectangular wave and second and third position detecting signals ofsecond-and third-phase rectangular waves, said first, second and thirdposition detecting signals being successively generated with a width of120 electrical degrees; switching elements connected to both ends ofsaid first-, second- and third-phase exciting coils; first diodesrespectively connected in a reverse direction to series-connectedcircuits of said switching elements and corresponding ones of saidfirst-, second- and third-phase exciting coils; an energizationcontrolling circuit means for setting said switching elementscorresponding to said first-, second- and third-phase exciting coils forperiods of time corresponding to the widths of the first, second andthird position detecting signals to energize said corresponding ones ofsaid first-, second- and third-phase exciting coils, said energizationcontrolling circuit means including DC power source means for generatinga driving torque; means for adjusting the position of said positiondetecting means and for fixing the position of said position detectingmeans so as to cause an output torque generated by energization of eachof said first-, second- and third-phase exciting coils to besubstantially at a maximum and substantially flat; transfer means forrapidly transferring magnetic energy stored on a preceding one of saidfirst-, second- and third-phase exciting coils into stored magneticenergy of a next one of said first-, second- and third-phase excitingcoils in a boundary portion between adjacent ones of said first, secondand third position detecting signals, said transfer means includingsecond diode means for preventing a reverse current and coupled to saidDC power source means in a forward direction so as to suppress torquereduction due to a rising portion in an initial period of energizationof each of said first-, second- and third-phase exciting coils and tosuppress generation of a counter torque due to an extension of a fallingportion in the terminal period of each of said first-, second- andthird-phase exciting coils; and means for causing the sum of magneticattraction forces in a radial direction between said salient poles andsaid first-, second- and third-phase magnetic poles of said first andthird fixed armatures and a magnetic attraction force in a radialdirection between said salient poles and said first-, second- andthird-phase magnetic poles of said second fixed armature to act inopposite directions and for maintaining a preset differencetherebetween.
 3. A three-phase reluctance electric motor, comprising:anouter casing; a rotation shaft rotatably supported by said other casing;a magnetic rotor fixed on said rotation shaft; salient poles projectingto an outer peripheral surface of said magnetic rotor, said salientpoles being disposed at a regular pitch; first, second and third fixedarmatures sequentially arranged in an axial direction and being fixed tosaid outer casing; a pair of first-phase magnetic poles of said firstfixed armature projecting from an inner peripheral surface of said firstfixed armature, each of said first-phase magnetic poles of said firstfixed armature being adjacent to the other and having an end portionfacing one of said salient poles with a predetermined gap between saidend portion and said one of said salient poles; a pair of second-phasemagnetic poles of said first fixed armature projecting from the innerperipheral surface of said first fixed armature, each of saidsecond-phase magnetic poles of said first fixed armature being adjacentto the other and being separated from a corresponding one of saidfirst-phase magnetic poles of said first fixed armature by 120mechanical degrees; a pair of third-phase magnetic poles of said firstfixed armature projecting from the inner peripheral surface of saidfirst fixed armature, each of said third-phase magnetic poles of saidfirst fixed armature being adjacent to the other and being separatedfrom a corresponding one of said first- and second-phase magnetic polesof said first fixed armature by 120 mechanical degrees; first-, second-and third-phase magnetic poles of said third fixed armature projectingfrom an inner peripheral surface of said third fixed armature, each ofsaid first-, second- and third-phase magnetic poles of said third fixedarmature being in a position corresponding to corresponding ones of saidfirst-, second- and third-phase magnetic poles of said first fixedarmature and having the same construction as corresponding ones of saidfirst-, second- and third-phase magnetic poles of said first fixedarmature; first-, second- and third-phase magnetic poles of said secondfixed armature projecting from an inner peripheral surface of saidsecond fixed armature, each of said first-, second- and third-phasemagnetic poles of said second fixed armature having the sameconstruction as corresponding ones of said first-, second- andthird-phase magnetic poles of said first fixed armature and beingdisposed in a position deviated by 180 mechanical degrees fromcorresponding ones of said first-, second- and third-phase magneticpoles of said first fixed armature.
 4. A three-phase reluctance electricmotor as recited in claim 3, wherein:each of said first-, second- andthird-phase magnetic poles of said second fixed armature having a widthin the axial direction equal to twice that of corresponding ones of saidfirst-, second- and third-phase magnetic poles of said first fixedarmature.